1. Field of the Invention
The present invention concerns a weft feeder for fluid jet looms, of the type which also measures the weft yarn lengths to be fed (measuring weft feeder) and wherein the weft yarn reserve winding unit or drum has an adjustable cross section.
More particularly, the invention concerns improvements in such a weft feeder, to allow a precise and efficient and, at the same time, easy and rapid adjustment of the cross section of the winding unit--satisfactorily adopted on an industrial level--and thus of the weft yarn lengths winding around the same.
It is known that, in modern weaving technique with fluid jet looms, use is commonly made, to feed the weft, of measuring weft feeders interposed between the yarn feed spool or reel and the loom.
Weft feeders of this type comprise an electric motor causing the rotation of a yarn distributing or winding arm, and a winding unit in the form of a drum, held stationary, around which the arm winds up the yarn into even turns, forming a weft yarn reserve the length of which is detected by means of suitable sensors.
The loom nozzle, preset to launch the weft yarn in the warp shed, draws from the weft feeder drum the yarn length required for each insertion.
This length is measured and controlled by the actual weft feeder by counting, with suitable means, the number of yarn turns being unwound.
As soon as the weft yarn at the outlet of the weft feeder and launched into the loom shed has reached the predetermined length, it is stopped on the weft feeder drum by means of a device--generally an electromagnetic device--comprising a rod apt adapted to engage and stop the yarn at the outlet of the winding unit. This rod is movable between a withdrawn rest position and a projecting yarn stopping position in which its end moves into a cavity formed on the drum periphery, close to its free end, to thereby stop the weft yarn which bears against the rod as it unwinds from the drum.
2. Description of the Prior Art
To measure the weft yarn length at each insertion, two different solutions are generally adopted:
the cross section of the winding unit (and thus the perimeter of the section--usually a circumference--and the length of the single yarn turns winding around the same) is kept constant, and a plurality of yarn stopping devices is mounted around the outlet end of the unit, so as to carry out a discrete measurement of the weft yarn length to be inserted in integer turn numbers and turn fractions;
or, alternatively,
the cross section of the winding unit (and thus the perimeter of the section--usually a polygon as close as possible to a circumference--and the length of the single yarn turns winding around the same) is varied, and a single yarn stopping device is mounted at the outlet end of said unit, so that the weft yarn length fed to the loom is always equal to an integer number of turns unwound from the unit, thereby obtaining a continuous measurement of the weft yarn length to be inserted at each beating up.
Both of these solutions have long been adopted in constructing measuring weft feeders for fluid jet looms. Obviously, they are not equivalent from the technical point of view, either as far as difficulties of construction and as far as performances.
The solution providing for a fixed cross section of the winding unit is currently preferred when more interest is placed in the quality of the winding of the reserve turns, in that it allows--without too many construction difficulties--to arrange and move forward the yarn turns separately on the winding unit; this characteristic is greatly appreciated and particularly advantageous when weaving highly twisted and very hairy yarns or parallel filaments with no twist.
On the other hand, the presence in the aforementioned solution of a plurality of yarn stopping devices increases the structural complexity and the cost of the measuring unit and, furthermore, it does not allow the continuous measurement of the weft yarn length to be inserted.
The solution providing for an adjustable cross section of the winding unit, and thus for an adjustable length of the yarn turns, is generally less complex from the constructional point of view. In fact, in this case, a single yarn stopping device is normally provided, which can thus be optimally realized with no problems of having to limit the costs and dimensions; in some cases, however, in order to reduce the adjustment range of the cross section perimeter of the winding unit, more yarn stopping devices are provided, through still of very reduced number (up to four).
On the other hand, the requirement to adjust the cross section of the winding unit does not allow to freely choose the system moving forward the yarn turns.
In fact, the systems generally adopted to obtain the advancement of the yarn turns are, above all, of the sliding forward type, wherein the turns being wound around the drum push forward the previously wound up turns, and of the oscillating disk type, wherein the yarn turns are moved forward one close to the other thanks to a disk positioned next to the winding arm, which performs an oscillating movement about the weft feeder axis.
The construction of a weft feeder for fluid jet looms, of the type having a winding unit with adjustable cross section in which the advancement of separate yarn turns is simultaneously obtained, combines the advantages of both previously described systems, although involving considerable structural complications.
It is known, in fact, that the system moving forward the yarn turns separately provides for a winding unit having a cage wall formed by fixed and, alternately, movable columns, wherein the reciprocating movement of said columns--caused by the rotation of the driving shaft--determines an axial advancement of the turns towards the outlet end of the drum, while positively keeping the turns mutually spaced.
A correct advancement of the yarn turns on the winding unit is determined by the mutual radial position of the columns, in that the movable columns partially and variably emerge from the periphery of the fixed columns, thanks to the motion imparted thereto by the weft feeder driving shaft.
The extent to which the movable columns emerge from the fixed ones determines the pitch or distance between the yarn turns and thus the number of turns which can be wound around the winding unit.
This is an important characteristic of the weft feeder, in that the number of yarn turns which can be stored on the drum determines the weft feeding capacity in meters per minute.
Thus, in a weft feeder having a winding unit with adjustable cross section and wherein the yarn turns are moved forward separately, it is necessary for the evenness of the pitch and of the forward motion of the turns to be kept constant when adjusting the cross section of the winding unit and its perimetral length.
A weft feeder for fluid jet looms of the type specified heretofore is known from FR-2626014. In this feeder, the adjustment of the radial displacement of the alternately fixed and movable columns, divided into four pairs of groups or sectors, is obtained by loosening fastening screws, by manually shifting each single group or sector of columns along radial slits, and by subsequently tightening the screws.
A manual adjustment is hence performed, which is not easy and quick to carry out especially for the following reasons:
The adjustment of the groups or sectors of fixed and movable columns has to be carried out individually, sector by sector, on each pair of sectors, with the risk of altering each time the reciprocal adjustment--which has to be particularly precise--between the sector of fixed columns and that of movable columns in each pair.
The reciprocal positioning of the groups or sectors of movable and fixed columns is anyhow left to the perception of the operator who carries out the adjustment.
The operations require considerable ability and long intervention times.
As can be noted, the solution of FR-2626014--although providing the undoubted advantages of a winding unit with adjustable cross section and yarn advancement in separate turns--does not answer the requirements of reliability and easiness of use which need to be satisfied in an industrial machine, especially if designed for the textile field, wherein the conditions of use are extremely strict and it is of primary importance to be able to perform any adjustment operations most easily.
On the basis of the above, it appears of evident interest to be able to provide a measuring weft feeder for fluid jet looms having a winding unit with adjustable cross section and yarn advancement into separate turns, wherein the cross section of the unit may be adjusted through a centralized control, namely wherein the operation of a single adjustment member is adapted to simultaneously shift all the fixed and movable columns alternately in the unit, keeping moreover constant their reciprocal position and ensuring the evenness of the pitch between the turns when adjusting the cross section of the winding unit and the length of the yarn turns wound thereon.